Electrodeposited chromium has a key role in providing the engineering needs of numerous manufactured products such as artillery pieces, gun barrels, and the like. The deposits in use are of two general classes: i.e. high contraction (HC) and low contraction (LC) chromium. The term "HC" stands for high contraction and refers to the tendency for as-plated hard chromium to shrink on heating. Due to its high hardness, high contraction chromium is commonly used as a protective coating to reduce galling and wear. Where corrosion is of concern, LC or low contraction chromium is used to take advantage of its crack-free and high strength characteristics. Conventional HC chromium deposits are weakened by the presence of cracks and are extremely brittle, while LC chromium deposits are much softer and therefore are susceptible to swaging under intense loading. It would be advantageous to produce deposits which combine the favorable characteristics of HC and LC chromium. One approach is through laminated plating.
The properties of laminated chromium have been observed in a number of studies and have been reported with reference to adhesion and crack formation. In all cases, the material cyclic nature of the plating process, current interruptions, or variations on plating temperature are responsible for the formation of the laminated structure. The present invention differs from all previous studies in that the laminations consist of alternating layers of two distinct types of chromium deposits rather than discontinuities brought about by a periodic current interruptions or current reversal. Through the use of a microprocessor-controlled plating system, the preparation of laminated deposits through programmed current modulation, and precise switching of plating solutions is made possible. In theory, such laminated structure should exhibit greatly altered mechanical properties, and a means of tailoring the strength and hardness of the deposit by varying the thickness of the various layers of high contraction and low contraction layers.